Currently, valves for regulating the flow of fluid in refrigeration systems have a structure that comprises                a valve body, provided with an inlet and an outlet for the fluid, which are connected by a connecting compartment,        a connecting compartment flow control device, inserted in an appropriately provided seat formed in the valve body.        
The flow control device comprises a connecting compartment flow control piston, which is functionally connected to an electric motor.
The piston is inserted partially in a cylinder, in which it can slide by way of the action of the electric motor, to which it is functionally connected by a screw-type actuator.
The electric motor modulates the degree of obstruction of the connecting compartment by the piston, making it slide along the sliding axis, defined by the axis of the cylinder, between two extreme positions, one for complete obstruction of the connecting compartment and one for maximum opening of the connecting compartment.
The obstruction device further comprises a tubular body that accommodates a fixed core, a rotary core and a stem for the actuation of the flow control piston, which compose the screw-type actuator.
The fixed core is welded to one end of the tubular body and supports rotatably the rotary core to which the stem is connected by way of a screw-and-nut coupling.
Such stem crosses axially the fixed core and can slide along it but not rotate thanks to a guided coupling.
The rotor of the motor is also accommodated in the tubular body and is jointly fixed to the rotary core in order to impart thereto a rotation that is converted by the screw actuator into a translational motion of the stem in the fixed core along the sliding axis.
Thus, upon actuation of the motor the position of the piston in the connecting compartment is modulated, determining the degree of its obstruction.
The cylinder inside which part of the piston slides is a sleeve that is welded to the fixed core, which is also equipped for connection to the valve body, for example by means of a threaded ring for connection to a threaded seat of the valve body or by means of a flange that can be fastened against a threaded shoulder of the valve body by a thrust ring, which is commonly known as crown.
The components of the obstruction device are therefore divided into                components that are fixed to the valve body, which are the tubular body and the cylinder, which are welded to the fixed core,        components that can be turned about the sliding axis, which are the rotor and the rotary core, and        components that can perform a translational motion along the sliding axis, which are the stem and the piston.        
One drawback of this structure is that in order to ensure the coaxiality of the stem with respect to the cylinder, in which the piston slides, it is necessary to have a sophisticated coupling providing coaxiality to the fixed core with the rotary core and with the sleeve that provides the cylinder.
Moreover, currently known regulating valves have balancing ducts that connect the front of the piston to a balancing chamber that it delimits within the cylinder.
Therefore, ensuring the absence of leaks from such chamber, by means of a reliable hermetic connection of the sleeve to the fixed core, is a currently felt need.
This connection is provided generally by welding, which by having to be accurate and free from defects that can compromise its tightness, is performed with high precision, to the full disadvantage of the low cost of production of this type of valve.